| Glaciers are sensitive indicators of climate change and natural solid reservoirs that provide important fresh water resources for runoff.The Qilian Mountains contain abundant glacier resources.Under the background of climate warming,the glaciers in the Qilian Mountains are shrinking in a large area,and the glacier change has a certain impact on regional water resources change.How to effectively monitor and evaluate the response of glacier change to climate and the impact of glacier change on local water resources is a key point of glacier research in the Qilian Mountains,which can provide scientific and effective suggestions for local ecological development and water resources utilization.In this study,the changes of glacier area and mass balance in the Qilian Mountains in the northeastern Tibetan Plateau were analyzed based on multi-phase remote sensing images and digital elevation model.Combined with meteorological factors and glacier attributes,the reasons for the temporal and spatial heterogeneity of glaciers in the Qilian Mountains were discussed.Based on the temperature index model,the annual mass balance of glaciers and melt water were simulated and the influence of glacier melting on runoff in different area of the Qilian Mountains was analyzed.The main conclusions of this paper are as follows:(1)The total number of glaciers in the Qilian Mountains is 2523,with an area of1470.05±97.99km~2in 2020.The number of glaciers<0.5km~2in scale are the majority,accounting for 74.60%of the total number of glaciers,but only 19.71%of the total area.The glaciers>1.0 km~2in scale have the largest area,accounting for 66.38%of the total area,but the number of glaciers only accounts for 13.83%of the total.Glaciers are distributed in the area of 4021-5769m asl,concentrated in the area of4700-5300m asl.The glacier area is the largest(1021.59km~2)in the area of4,900-5100m asl,and the smallest(20.10km~2)in the area of above 5300m asl.The average slope and number of glaciers showed obvious normal distribution.Most glaciers in the Qilian Mountains developed in slope between 20°and 35°,accounting for 77.30%of the total glaciers.The Qilian Mountains are divided into eastern,middle and western sections,with glacier areas of 49.41km~2,752.17km~2and668.47km~2respectively.The region is also divided into 11 river basins,among which Shule River Basin(5Y44)has the largest area and number of glaciers,with 624glaciers and an area of 471.09km~2.Bayan Gol River Basin(5Y59)has the least area and number of glaciers,with 9 glaciers and an area of only 1.85km~2.(2)From 1970s to 2020,a total of 298 glaciers in the Qilian Mountain disappeared,with an area shrinking of 516.89km~2,and the average retreat rate was0.54%a-1.The average area of glaciers decreased from 0.70km~2to 0.58km~2.The retreat rates of glacier area at different scales were calculated,and the results showed that glaciers at all scales showed significant regression,and the area change rate decreased with the increase of glacier size.The altitude of the glacier concentration area increased gradually in the eastern and middle parts of Qilian Mountains,but almost unchanged in the western part.The change of glacier area increased firstly and then decreased with the increase of altitude.At the basin scale,the eastern basin has the smallest glacier retreat area but the highest glacier retreat rate.(3)From 2000 to 2014,the mean elevation of glacier surface decreased by5.13±0.56m(0.37±0.04m a-1),indicating significant ice loss,and the mean glacier loss was 0.31±0.04m w.e-1.With the increase of altitude,the rate of glacier loss gradually decreases.The decrease rate of glacier surface elevation at 4100m asl is the largest.When the altitude is close to 5300m,the change of glacier surface elevation tends to zero.The glacier thinning rate in the eastern part is the fastest,followed by the middle part,and the lowest in the western part,with the average thinning rates of 0.61±0.04m a-1,0.43±0.04m a-1and 0.27±0.04m a-1,respectively.On basin scale,the glacier in Datong River basin decreased the most rapidly with-0.62±0.06m a-1(-0.53±0.06m a-1),and the glacier in Iqe River-Tatalin Gol River basin decreased the least with-0.15±0.05m a-1(-0.13±0.05 m a-1).(4)The glacier area and mass balance of Qilian Mountains showed significant temporal and spatial differences,which were influenced by many factors.The mean summer air temperature and precipitation in Qilian Mountains increased significantly(0.56°C/10a and 13.2mm/10a,respectively)from 1979 to 2018.The spatial difference of temperature change increased significantly from east to west,and the rapid warming area was concentrated in the east.The variation of precipitation is complex,with a slight decrease in eastern and a gradual increase from east to west and north to south.The average size of glaciers in the east and west is 0.32 km~2and 0.78 km~2respectively.The lowest altitude is 4380m asl in the east and 4818m asl in the west.The combined action of these factors resulted in different glacier changes in different regions.(5)By using the distributed temperature index model,the mean mass balance of Qilian Mountains glaciers is-8.76m(-7.45m w.e.)from 1990 to 2017,but positive accumulation occurred in some years(1992-1993).The overall trend is decreasing,reaching the peak value of-552.85mm w.e.in 2016.The mean annual accumulation and ablation of glaciers were 266.30mm w.e.and 532.35mm w.e.respectively.The effect of glacier ablation on mass balance was more significant than that of mass accumulation.The mass balance of all basins showed a decreasing trend.The sensitivity of mass balance in the western part of the glacier to temperature is significantly lower than that in the middle and eastern parts,which is related to glacier size.(6)From 1990 to 2017,the total glacier loss of Qilian Mountains was about1.36×1010m~3,and the total melting water was about 22.2Gt(0.81Gt a-1).The annual change of glacier melt water showed a trend of first increasing and then decreasing,and reached the peak in 2010.On basin scale,the glacier area in the Shule River Basin is the largest,and the corresponding glacier runoff is also larger than other basins,indicating that there is a significant positive correlation between glacier melt water and glacier area.(7)The glacial meltwater accounted for 4.6%,4.4%and 9.7%of the total runoff in the Jiutiaoling,Sunan and Danghe basins,respectively.Glacial meltwater accounts for a higher proportion of runoff in drought years,reflecting the ability of glaciers to regulate rivers.The results of MPR show that the MPR ranges from 0.05%to 7.8%in each basin,and the MPR is higher in the western region,indicating that glacial meltwater plays an important replenishment role in the arid area of the Qilian Mountains.According to the results of the annual variation of glacier melt water during the study period,the glacier melt water in Qilian Mountains may have reached the peak,and the rivers mainly fed by glaciers will be greatly affected,and the phenomenon of river interruption and extinction may occur in the future. |
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